This invention relates to an electric arrangement for starting and operating an electric discharge lamp and, more particularly, to a compact igniter circuit for a discharge lamp of the type having preheatable electrodes.
It is known to use a glow discharge starter device for igniting discharge lamps. This results in a simple and inexpensive igniter device which is relatively reliable in operation. However, a glow discharge starter will not work well in situations where the lamp operating voltage is relatively close to the nominal AC supply voltage. For example, in the case of a discharge lamp with an arc voltage of 90 volts intended for use with a 115 volt AC supply voltage, the conventional glow discharge starter device will not provide reliable lamp ignition, although operation of such a lamp from a 220 volt AC supply voltage is quite reliable. In other words, a glow discharge starter device operates well if there is a relatively large difference between the nominal value of the line voltage and the characteristic lamp operating voltage.
One solution to this problem is to use an electronic igniter-ballast circuit in place of the glow discharge starter. A disadvantage of this solution is that the electronic igniter-ballast circuit is more expensive than a ballast-igniter circuit that utilizes a glow discharge starter device.
An electronic igniter-ballast apparatus for starting and operating one or more discharge lamps wherein the total arc voltage of the tube(s) differs only a little from the AC supply voltage is described in U.S. Pat. No. 4,253,043 issued 2/24/81 to Chermin et al. This apparatus includes a bidirectional controlled semiconductor switching element connected in series with a PTC resistor across the preheatable electrodes of the discharge tube(s). A VDR element is connected in a control circuit of the semiconductor switching element to ensure that the discharge tube(s) does not ignite before the tube electrodes are heated sufficiently. The PTC resistor heats up to limit the current flow through the preheatable electrode if the discharge tube(s) fails to ignite.
U.S. Pat. No. 4,087,723 issued 5/2/78 to Chermin et al describes an arrangement for starting and operating a discharge lamp provided with cold electrodes. A capacitor, a PTC resistor and a controlled bidirectional semiconductor switching element are serially connected across the lamp electrodes to form a starter circuit for the lamp. If the lamp fails to ignite, the PTC resistor heats up and switches over to its high resistance state so that the arrangement produces substantially no radio interference.
A circuit arrangement for starting and operating a discharge lamp by means of an electronic ballast is described in U.S Pat. No. 4,358,711, 11/9/82 in the name of H. Bex. This circuit includes an electronic switch (transistor) in series with the lamp to act as a ballast to limit the lamp operating current. A series circuit consisting of a PTC resistor and an ohmic resistor is connected in parallel with the electronic switch, with only the PTC resistor connected in parallel with a control circuit of the electronic switch. The PTC resistor and ohmic resistor allow line frequency current to flow through the lamp electrodes for approximately 1/2 to 1 second to preheat the electrodes. The PTC resistor heats up, changes its resistance state, thereby initiating high frequency operation of the electronic switch and ignition of the discharge lamp.
It is also known to use a PTC resistor in combination with a glow discharge starter device for igniting and operating a discharge lamp. U.S. Pat. No. 3,740,609 issued 6/19/73 to J. C. Moerkens describes such an arrangement for igniting a discharge lamp which has such a high ignition voltage that it cannot be ignited properly by means of a conventional glow discharge starter. The glow discharge starter is connected in series circuit with the lamp ballast and the preheatable electrodes of the lamp across the supply voltage terminals. A diode and a PTC resistor are serially connected in shunt with the lamp to effect a voltage doubling that promotes ignition of the lamp. After the lamp ignition, the PTC resistor heats up and effectively renders the diode branch circuit inoperative.
Another PTC resistor and glow discharge starter combination for operation of a discharge lamp is shown in U.S. Pat. No. 4,208,616 issued 6/17/80 in the name of J. C. Moerkens. The PTC resistor is connected in series with the glow discharge starter in the preheat circuit of the lamp electrodes. The PTC resistor receives current only during the starting procedure of the lamp and will not switch over to its high resistance state if the lamp ignites normally. If the lamp does not ignite, the PTC resistor heats up and switches to its high resistance state and thereby limits the current in the lamp ballast and the lamp electrodes to a safe value.